There are more than 90 prisoners currently on 'lockdown' at Mountjoy Prison, new figures show.

Justice Minister Frances Fitzgerald said that the 91 prisoners under the restricted regime at the Dublin prison account for almost a third of the 300 prisoners on 'lockdown' across the Irish Prison Service.

The figures show the vast majority of those facing restrictions in Mountjoy are on a 19-hour restricted programme, with five in their cell for 21 hours and three on 23-hour lockdown.

"The restriction of a prisoner's regime can occur due to a number of factors, including the protection of vulnerable prisoners," said Ms Fitzgerald.

At Limerick prison, there are 61 prisoners on 21-hour lockdown, with a further 54 at Wheatfield.

Separately, the minister confirmed that 304 prisoners still had to slop out in their cells.